Re: [Haskell-beginners] Help me with designing my daemon, please.

I need to provide more detail. Keep in mind that what I want to do, and the way I'm doing it may not fit at all. This code is using Chans and MVars, but could be using TChans and TVars easily enough. I kept things the way they are to just express what I'm trying to do

data ServerModel = PRODUCT1 | PRODUCT2 | PRODUCT3 | PRODUCT4 | PRODUCT5 deriving Show

newtype ProcessStep = PStep (ServerModel -> FilePath -> IO ())

type Cookie = String

type ProcessState = MVar ([ProcessStep],ProcessConfig)

data ProcessConfig = PConfig { model :: ServerModel , ipAddress :: String , rootDirectory :: FilePath , cookie :: Cookie } deriving Show

preProcess :: ServerModel -> FilePath -> IO () preProcess sModel fPath = putStrLn ("preProcessing" ++ show sModel)

initiatedJob :: ServerModel -> FilePath -> IO () initiatedJob sModel fPath = putStrLn ("in progress" ++ show sModel)

makeChart :: ServerModel -> FilePath -> IO () makeChart sModel fPath = putStrLn ("chart making" ++ show sModel)

main :: IO () main = do pState <- make world <- newEmptyMVar :: IO (ProcessState) worldQueue <- newChan :: IO (Chan ProcessState) installHandler userDefinedSignal2 (Catch $ worldHandler world worldQueue) N othing installHandler userDefinedSignal1 (Catch $ emptyQueue worldQueue ) Nothing ---- This is for testing purposes. I just want to be able to empty the Chan and see if expected behavior holds installHandler nullSignal (Catch $ emptyMVar world ) Nothing ---- For testing as well, same reason as above. sequence_ $ repeat $ queueCheck

worldHandler :: ProcessState -> Chan ProcessState -> IO () worldHandler world worldQueue = do

mvarState <- isEmptyMVar world let tStep = PStep undefined let tConfig = PConfig { model = undefined, ipAddress = undefined, rootDirectory = undefined, cookie = undefined }

let tState = undefined case (mvarState) of True -> putMVar world tState False -> growQueue where growQueue = do newWorld <- newMVar ([tStep], tConfig) writeChan worldQueue newWorld

On Wed, Sep 7, 2011 at 1:37 PM, David McBride wrote:

I'm imagining this:

data TestInfo = {  testname :: String,  etc.. } data TestResult = {  success :: Bool,  etc... }

data Test = Test (TestInfo -> IO ()) type Tests = [Test]

main = do  let tests = [whatever] :: Tests  testchan <- newTChanIO :: IO (TChan TestInfo)  resultchan <- newTChanIO :: IO (TChan TestResult)  exceptionwhatever $ queuetest testchan  forkIO $ testThread (testchan,resultchan) tests  printTestResults resultChan

queuetest chan = atomically $ writeTchan (TestInfo .....)

testThread (testchan, resultchan) tests = forever $ do  newtest <- atomically $ readTChan testchan  results <- mapM tests newTest  atomically $ writeTChan resultchan results

printTestResults chan = forever $ do  x <- atomically $ readTChan chan  print x

Something like that perhaps?

On Wed, Sep 7, 2011 at 3:31 PM, Michael Litchard wrote:

...

This is what I am trying to do. I have tests to run and manage. I'm only running one test at a time. When my daemon gets a signal, it will either prep a test and run it, or queue the request. After it runs the test, I want it to check the queue for other tests that may have been requested. This is my first expedition into this domain. I'm trying to collect MVars and putting tem in a TChan is the way that seemed right, but I'm not sure at all. This is my first guess. I thought I needed a forked thread for the eventuality that I get a signal while my transaction is being executed. Have I clarified or further obfuscated?

On Wed, Sep 7, 2011 at 12:22 PM, David McBride wrote:

...

It sounds bizarre.  Why pass around an mvar in tchan, when you could just pass a maybe around and pattern match to see if it is Nothing or not?  Also, why have forkio and tchan at all if they are only going to operate in sequence, one at a time?

What exactly are you trying to do?

On Wed, Sep 7, 2011 at 3:01 PM, Michael Litchard wrote:

...

I have a daemon I need to build, and need to work out some design details I am having difficulty with. Here's what the design looks like right now

When the daemon starts it creates an empty MVar and an empty TChan. Then it listens for a usrSIG1. when it gets one, it checks to see if the MVar is empty. If it is, it does some stuff to fill the MVar, which is then used to pass around state for a list of functions. These functions are always the same. After evaluating these functions, the TChan is checked. As long as the TChan has something in it, it populates an MVar and the same three functions are evaluated in the same order again.

If the MVar is full, it creates another MVar of the same type and puts it in the TChan.

Is this a sound design? Does it prompt any questions from you? Here's my question. If this is basically a sound design, I know I will need use forkIO. I'm not sure where. If this is not a sound design, please ask questions or give other feedback so I can make changes and restore sanity.

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